Fig. 4. CXCR4 expression determines T cell dark zone positioning.

a, Experimental outline of in vitro 4-OH-tamoxifen treatment of CD4⁺ T cells isolated from Cxcr4^fl/fl; Rosa26^ERT2Cre/+ OT-II mice that were treated for 48 h, after which the cells were transferred into adult B6SJL recipient mice. Recipient mice were immunized subcutaneously with OVA in alum and analysis was performed after 10 d. b, Representative ×20 magnification confocal images of the GCs from the iLNs of B6SJL mice that received tamoxifen-treated OT-II cells from either Cxcr4^fl/fl; Rosa26^+/+ or Cxcr4^fl/fl; Rosa26^ERT2Cre/+ mice; scale bars, 100 µm. LN sections were stained for IgD (green), CD35 (white), Ki67 (blue) and CD45.2 (magenta). c–h, Quantification of the GC area (c), the number of CD45.2⁺ transferred cells in the GC (d), percentages of OT-II T_FH cells in the CD35⁺ FDC light zone area (e) and Ki67⁺CD35⁻ dark zone area (f), percentage of the GC occupied by the CD35⁺ FDC network (g) and percentage of the GC occupied by the dark zone (h), from the iLNs of recipient B6SJL mice (n = 10). Data are representative of two independent experiments performed with biologically independent samples. In graphs, bar heights represent the median and P values were obtained by performing an unpaired, two-tailed Mann–Whitney U test. Each symbol represents a single mouse. LZ, light zone. DZ, dark zone.

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